Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Zoology and Genetics

First Advisor

Peter A. Peterson


The mutability of transposable element-induced unstable alleles is controlled in one of two ways. If the locus contains an active autonomous element, the allele is under autonomous control (one component system). If the locus contains a defective element, the allele is under non-autonomous control (two component system). In maize, eight genetically defined two-component systems exist;Two different factors control mutability of an unstable allele (c2-m881058Y) of the C2 gene of maize. Both an autonomous En/Spm element and an unrelated independent factor, named Mediator, are coordinately required for the excision of the defective element at c2-m881058Y. According to genetic analysis, Mediator does not have the suppressor (S) function or mutator (M) function of En/Spm. Mediator has no effect on the timing or frequency of excision of En1, En-low, or various I/dSpm elements. Mediator is not an autonomous element of another transposable element system in maize. Hence, Mediator only mediates a specific interaction between En and the insert at c2-m881058Y. Molecular analysis of c2-m881058Y has revealed a 3.3-kb complex, En-related defective element inserted into the second exon of the C2 gene. The ends of this element are homologous to the ends of En/Spm, but an internal 1.7-kb region shows no En/Spm homology. Many nucleotide changes (11%-14%), relative to En1, occur within and between the 12-bp TNPA binding motifs. Alterations of these critical cis-determinants may account for the need for a "helper" factor for excision. This element is named Irma, for Inhibitor that requires Mediator also, and represents a unique, low-copy class of receptor element.



Digital Repository @ Iowa State University,

Copyright Owner

Michael Gerard Muszynski



Proquest ID


File Format


File Size

132 pages

Included in

Genetics Commons